He said there had been a "significant number of occasions in the last year or so on which I have disagreed with the Number 10 policy line".

Davis added that he had previously decided to toe the line and remain in the Cabinet "because I considered it was still possible to deliver on the mandate of the referendum, and on our manifesto commitment to leave the Customs Union and the Single Market".

But he also delivered a damning verdict on the PM's recent approach, writing: "I am afraid that I think the current trend of policy and tactics is making that look less and less likely."

Davis arrives in Downing Street for talks on his role as Brexit Secretary with Theresa May

May had hoped the Cabinet agreement for a soft Brexit would help her deliver the "right Brexit" for the UK, with an offer to Brussels to share a "common rulebook" on goods and form a new UK-EU free trade area.

But Mr Davis lashed out at the proposals just 48 hours after being part of the Cabinet that agreed them.

He has previously rowed with the PM over whether Britain should be tied to EU customs rules indefinitely.

He is understood to be deeply unhappy and frustrated with the slow process of Brexit decision-making.

But his fury grew after May refused to define a precise time limit for a backstop solution to keep the Irish border open.

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When else has David Davis threatened to stand down?

David Davis has threatened to resign on a number of occasions as Brexit Secretary.

April 2018, rumours claimed Davis was on the verge of quitting over customs union disagreements. His friends told the Daily Express that he was "extremely frustrated" with the Government's approach to Brexit.

December 2017, Davis said he would quit if his friend Damian Green was sacked over pornography allegations.

November 2017, Davis was forced to deny rumours he could quit, after he was enraged at Boris Johnson and Michael Gove's involvement in Brexit.